PROJECT SUMMARY The overall goal of Project 4 is to better understand the relationship between the observed concentrations in air and sources of airborne PCBs and their breakdown products in ambient and indoor environments. Project 4 provides a path for significant and measureable reduction of human risk through exposure to PCBs and their breakdown products, through significant and measureable improvements in the ability to detect, predict, and attribute these compounds and to assess airborne exposure risks. We further propose to identify the ability of contemporary PCB mitigation methods to reduce population-scale airborne exposure to PCBs. The central hypothesis for Project 4 is that emissions of airborne PCBs and their breakdown products are a function of measureable and quantifiable characteristics of the compounds and environmental matrices on which PCBs reside. A corollary hypothesis is that the effectiveness of remediation efforts is dependent on the successful identification and quantitative characterization of emission sources. The aims of Project 4 are organized around field studies, state-of-the-art analytical tools and environmental modeling in urban and rural ambient outdoor and indoor environments to quantify sources, emissions, chemical transport, exposure, and fate. The aims of Project 4 are the following: Aim 1: Determine sources of airborne Aroclor and non-Aroclor congeners in urban air. Measurements of airborne PCBs and OH-PCBs; development of chemical transport models; and assessment geographic databases will be used to achieve this aim. Aim 2: Characterize the release of airborne PCBs in the Indiana Harbor and Ship Canal. Measurements of PCBs and OH-PCBs in sediment, water and air; laboratory experiments that reproduce environmental conditions; and chemical mass balance modeling will be conducted. Aim 3: Identification of sources of PCB congeners in indoor air. This aim includes determination of PCB congeners in building materials and manufacturing processes that produce PCBs found in homes. Aim 4: Determination of physical-chemical properties of PCB breakdown products. Laboratory experiments and computational models will be utilized to determine equilibrium and kinetic constants of these compounds.